JP2004336079A - Manufacturing method for compound single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method through which a compound single crystal with a lower plane defect density can be obtained, which is a method to manufacture compound semiconductor single crystals such as silicon carbide, gallium nitride, etc. by using the epitaxial growth method. <P>SOLUTION: Onto the surface of a single crystal substrate, two or more layers of a compound single crystal layer that is the same as, or different from, this substrate are grown in sequence through the epitaxial method. At least, part of the substrate's surface has multiple undulations extending in one direction, and the epitaxial growth at and after the second time is performed after forming multiple undulations extending in one direction onto at least part of the surface of a compound single crystal layer formed immediately before. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a compound single crystal including a silicon carbide single crystal useful as an electronic material. In particular, the present invention relates to a method for manufacturing a compound single crystal (for example, a semiconductor) including a silicon carbide single crystal having a low defect density or a small crystal lattice distortion, which is preferable for manufacturing a semiconductor device.

  Conventionally, silicon carbide growth has been classified into bulk growth by sublimation and thin film formation by epitaxial growth on a substrate. In bulk growth by the sublimation method, hexagonal (6H, 4H, etc.) silicon carbide which is a polymorph of a high-temperature phase can be grown, and a substrate of silicon carbide itself has been realized. However, defects (especially micropipes) introduced into the crystal are extremely large, and it is difficult to increase the substrate area. On the other hand, when the epitaxial growth method on a single crystal substrate is used, the controllability of impurity addition is improved, the substrate area is increased, and the micropipes, which are problems in the sublimation method, are reduced. However, in the epitaxial growth method, an increase in stacking fault density due to a difference in lattice constant between the substrate material and silicon carbide has often been a problem. In particular, silicon, which is generally used as a substrate to be grown, has a large lattice mismatch with silicon carbide. Therefore, twins (Twin) and anti-phase boundary (APB) in the silicon carbide growth layer. This is one of the causes of leakage current and the like, and has impaired the characteristics of silicon carbide as an electronic element.

As a method of effectively reducing the antiphase region boundary surface, K. Shibahara et al. Reported that a silicon (001) surface whose surface normal axis was slightly inclined (introducing an off angle) from the <001> direction to the <110> direction. A method of growing on a substrate (see FIG. 3) has been proposed. (Applied Physics Letter 50, 1987, p. 1888). In this method, since the steps at the atomic level are introduced at equal intervals in one direction by giving a slight inclination to the substrate, the vapor-phase growth method causes epitaxial growth by a step flow, and is perpendicular to the introduced steps. This has the effect of suppressing the propagation of surface defects in the direction (direction crossing the step). Therefore, as the thickness of silicon carbide increases, of the two types of anti-phase regions included in the film, the anti-phase region that expands in a direction parallel to the introduced step is the anti-phase region that expands in the orthogonal direction. Since the enlargement is performed preferentially as compared with the phase region, the boundary surface of the anti-phase region can be effectively reduced. However, as shown in FIG. 4, this method causes undesired formation of the anti-phase region boundary surface 1 and twin due to the increase in the step density at the silicon carbide / silicon substrate interface, and the anti-phase region boundary surface There is a problem that it cannot be completely resolved. In FIG. 4, reference numeral 1 denotes an anti-phase region boundary surface generated at a single atom step of the silicon substrate, 2 denotes an anti-phase region boundary surface meeting point, 3 denotes an anti-phase region boundary surface generated at a silicon substrate surface terrace, θ indicates the off angle, and φ indicates the angle (54.7 °) formed between the Si (001) plane and the boundary surface of the anti-phase region. The anti-phase region boundary surface 3 generated on the surface terrace of the silicon substrate disappears at the anti-phase region boundary surface meeting point 2, but the anti-phase region boundary surface 1 generated at the single atom step of the silicon substrate has no association partner. Does not disappear.
K. Shibahara et al., Applied Physics Letter 50, 1987, 1888.

  As a method for reducing such a plane defect (Twin, APB) in silicon carbide, the present applicant has provided an undulation extending in one direction parallel to the surface of a silicon substrate, and the surface of the silicon substrate has been subjected to undulation processing. A technique for eliminating surface defects propagating in silicon carbide by epitaxial growth of silicon carbide was proposed (Japanese Patent Application Nos. 2000-365443 and 11-288844). The effect of providing the undulating shape on the silicon substrate is that the off slopes are arranged on the silicon substrate so as to face each other as shown in FIG. 5, so that the facing surface defects associate with each other as shown in FIG. It is something that works.

  According to this method, silicon carbide in which surface defects have been largely eliminated can be obtained. However, when opposing surface defects meet and disappear, one of the associated surface defects remains and continues to propagate. In the case of a realistic undulation shape on a silicon substrate and the thickness of silicon carbide, for example, the undulation interval is 2 μm and the thickness of silicon carbide is 200 μm, the residual surface defect density is simply calculated (one surface defect remains from one undulation). (Assuming propagation) at least about 30 lines / cm. In order to completely eliminate these problems, a plate thickness that is 1.41 times the diameter of silicon carbide is required (thickness until the point where the end of the surface defect has completely propagated is no longer the growth surface). When the method is used, the growth time is too long, and the thickness becomes unrealistic.

  Also, compound semiconductors such as gallium nitride other than silicon carbide are expected as materials for blue LEDs and power devices. In recent years, there have been many reports of growing gallium nitride on silicon carbide substrates. This is because the use of silicon carbide as a base substrate for growing gallium nitride has advantages such as easy formation of electrodes, easy heat dissipation, and easy handling and processing because the cleavage direction of the crystal is the same. . However, it is difficult to obtain a large-area, high-quality silicon carbide substrate, and even if silicon carbide has a relatively small difference in lattice constant, plane defects propagate to the gallium nitride growth layer due to lattice mismatch at the interface. That is a challenge. As with the growth of silicon carbide on a silicon substrate, measures must be taken to eliminate defects.

  Therefore, an object of the present invention is to provide a method for producing a compound semiconductor single crystal such as silicon carbide or gallium nitride by using an epitaxial growth method, which method can obtain a compound single crystal having a lower plane defect density. Is to do.

The present invention for solving the above problems is as follows.
(1) A method for producing a compound single crystal in which two or more layers of the same or different compound single crystal layers are sequentially epitaxially grown on the surface of a single crystal substrate,
At least a portion of the substrate surface has a plurality of undulations extending in one direction, and the second and subsequent epitaxial growths extend in one direction on at least a portion of the surface of the compound single crystal layer formed immediately before. Performing the method after forming a plurality of undulations.
(2) The compound single crystal layer is a compound single crystal different from the single crystal substrate, and the compound single crystal forming the compound single crystal layer and the single crystal forming the single crystal substrate have a similar spatial lattice (1). )).
(3) The direction of the plurality of undulations extending on the surface of the single crystal substrate and the direction of extension of the undulations provided on the surface of the compound single crystal layer formed on the surface of the substrate are the same or orthogonal (1) or The production method according to (2).
(4) The manufacturing method according to any one of (1) to (3), wherein the extending directions of the plurality of undulations provided on the surface of the compound single crystal layer provided adjacent to the growth direction are the same or orthogonal.
(5) The method according to any one of (1) to (4), wherein the single crystal substrate is single crystal SiC.
(6) The method according to any one of (1) to (5), wherein the compound single crystal layer is single crystal SiC, or gallium nitride, aluminum nitride, or aluminum gallium nitride.
(7) The single crystal SiC substrate is cubic SiC whose basal plane is (001) plane or hexagonal SiC whose basal plane is (11-20) plane or (1-100) plane ( The production method according to any one of 1) to (6).

  According to the present invention, there is provided a method for producing a compound semiconductor single crystal such as silicon carbide or gallium nitride by using an epitaxial growth method, which method can obtain a compound single crystal having a lower plane defect density. be able to.

In the method for producing a compound single crystal of the present invention, two or more layers of the same or different compound single crystal layers are sequentially epitaxially grown on the surface of a single crystal substrate.
And, as the single crystal substrate, a substrate provided with a plurality of undulations extending in one direction on at least a part of the substrate surface (hereinafter, sometimes referred to as undulating single crystal substrate), using the second and subsequent times The epitaxial growth is performed after forming a plurality of undulations extending in one direction on at least a part of the surface of the compound single crystal layer formed immediately before.

  When a single crystal is stacked on the surface of the undulating single crystal substrate, the difference in height of the undulation is gradually eliminated, and a smooth mirror surface with a thickness of the single crystal layer of about several tens μm is obtained. Therefore, when the film thickness is more than that, the growth is caused by the two-dimensional nucleation due to the low step density. If the propagating surface defect propagating from the interface remains, it continues to propagate to the growth surface until it associates with the opposing surface defect.

  According to the manufacturing method of the present invention, a single crystal layer is formed on the surface of the undulating single crystal substrate by epitaxial growth, and the undulating process is performed again on the surface of the single crystal layer. As a result, the polar plane that has appeared on the base surface of the single crystal layer is once removed, and step flow growth is caused by the newly formed off-slope effect of the undulation. Then, the growth from the step to the terrace width direction becomes dominant, and the effect of suppressing the propagation of surface defects from the interface can be obtained. As a result, surface defects can be reduced as compared with a method in which a single crystal layer is formed on the surface of a single crystal substrate subjected to undulation processing. In the method of forming a single-crystal layer on the surface of a single-crystal substrate subjected to undulation processing, it was necessary to wait for plane defects to naturally associate with each other and eliminate them. The defect can be eliminated at an early stage as compared with the method of (1).

  Examples of the single crystal for the single crystal substrate include single crystal SiC. More specifically, the single crystal SiC substrate is cubic SiC whose basal plane is a (001) plane, or Hexagonal SiC whose basal plane is the (11-20) plane or the (1-100) plane can be used. As other single crystal substrates, for example, a single crystal Si substrate can be mentioned.

  Examples of the crystal constituting the compound single crystal layer include SiC, gallium nitride, aluminum nitride, aluminum gallium nitride, indium gallium nitride, and the like.

The method for producing a compound single crystal of the present invention is a method for producing a compound single crystal layer which is the same as or different from a single crystal substrate, but when the compound single crystal layer is a compound single crystal different from the single crystal substrate, This is particularly effective when the compound single crystal forming the crystal layer and the single crystal forming the single crystal substrate have a similar spatial lattice.
When two single crystals have a similar spatial lattice, it means that the positions of the atoms of the structural units (basic unit structure) of the crystals are similar, the bonding directions between the atoms are also the same, and the same crystal axis is used. It means to grow in the direction (epitaxial growth).
Examples of two single crystals having a similar spatial lattice include, for example, cubic GaN / cubic SiC, hexagonal GaN / hexagonal SiC, hexagonal AlN / hexagonal SiC, hexagonal AlGaN / hexagonal SiC, Cubic AlN / cubic SiC, hexagonal (4H) SiC / hexagonal (6H) SiC, and the like can be given.

The undulation processing performed on the surface of the single crystal substrate and the undulation processing performed on the surface of the single crystal layer will be described.
The undulations provided on the surface of the single crystal substrate and the undulations provided on the surface of the single crystal layer are a plurality of undulations extending in one direction, and reduce surface defects such as an antiphase region boundary surface in the single crystal layer. There is no particular limitation as long as it can be eliminated, and more specifically, undulations that can obtain the effect of introducing the off-angle shown by K. Shibahara et al. On the slope of each undulation. However, the undulations in the present invention are not required to have mathematically strictly parallelism or mirror symmetry, and have a form sufficient to effectively reduce or eliminate surface defects. You only need to have it.

For example, the undulation has a center line average roughness in a range of 3 to 1000 nm, and the inclination of the slope of the undulation is an angle smaller than the angle formed between the growth substrate surface and a generated surface defect such as a twin band. be able to. For example, in a cubic crystal layer, the angle formed between the {111} plane, which is the plane of the defect to be eliminated, and the (001) plane, which is the growth plane (horizontal plane), that is, an inclination of 54.7 ° or less, preferably 1 It can have a slope in the range from 5 ° to 54.7 ° (see FIG. 7). In the case of a hexagonal crystal, for example, the angle can be smaller than the angle formed by {1-101} (the angle depends on the lattice constant of the crystal) with respect to the growth plane (0001). Further, the angle with respect to the M plane (01-10) or the R plane (1-102) can be equal to or smaller than the angle formed by the C axis (0001).
Some examples of the growth surface and the generated surface defect have been described, but these are only examples, and the slope is not limited to the above. If the undulation has an inclination smaller than the angle formed between the growth surface and the generated surface defect, the undulation effect can be obtained. That is, it is sufficient that the surface defect generated from the opposing slope collides with the opposing surface defect and is at an angle sufficient to eliminate the defect.

Further, in the undulation, in a cross section orthogonal to a direction in which the undulation extends, a shape of a portion where slopes are adjacent to each other may be curved.
The undulations here are formed by the repetition of peaks and valleys, and are not so-called atomic steps, but have dimensions that are more macroscopic than atomic steps, as described below. Such undulations are, for example, undulations whose center line average roughness is in the range of 3 to 1000 nm, and the peaks are 1 to It may have a slope with a slope of 54.7 °. When the center line average roughness is 3 nm or more, an effective off angle is easily obtained, and the density of occurrence of surface defects is reduced. Further, when the center line average roughness is 1000 nm or less, the probability that the surface defects collide with each other and be eliminated increases. The center line average roughness is desirably 10 nm or more, and desirably 100 nm or less.

  The center line average roughness of the substrate surface is the center line average roughness (Ra) defined in B0601-1982 (JIS Handbook 1990), and the measured length L is measured in the direction of the center line from the roughness curve. When the center line of the extracted part is X axis, the direction of the vertical magnification is Y axis, and the roughness curve is represented by y = f (x), the value represented by the following equation is expressed in (μm) Refers to what is expressed.

  In the definition of JIS B0601-1982, the unit of the center line average roughness is μm, but in the present invention, nanometer (nm) is used. Further, a roughness curve for determining the center line average roughness (Ra) is measured using an atomic force microscope (AFM).

Further, it is preferable that the slope of the undulating slope is in the range of 1 ° or more and 54.7 ° or less.
In the method of the present invention, the effect is exhibited by promoting the growth of a compound single crystal such as silicon carbide in the vicinity of an atomic step on the surface of the substrate to be grown or the surface of the single crystal layer. The present invention is realized in the case where the slope of the (111) plane in which the entire slope is covered in a single step is 54.7 ° or less.
Further, when the inclination is less than 1 °, the step density of the undulating slope is significantly reduced, so that the inclination of the undulating slope is 1 ° or more. Further, it is preferable that the inclination angle of the undulating slope is not less than 2 ° and not more than 10 °.
In the present invention, the “undulating slope” includes all forms such as a flat surface and a curved surface. Further, in the present invention, "the slope of the undulating slope" means the substantial slope of the slope which contributes to the effect of the present invention, and means the average slope of the slope. The average inclination means an angle (an average value of an evaluation area) at which a crystal orientation plane and a slope of a substrate surface or a single crystal layer surface intersect.

  Further, in a cross section orthogonal to the direction in which the undulations extend, it is preferable that the shape of a portion where slopes existing on the surface of the substrate or the single crystal layer are adjacent to each other is curved. The portions where the slopes are adjacent to each other are the portion of the undulating groove and the ridge extending to the surface, and the cross-sectional shape of both the bottom portion of the groove and the top of the ridge is curved. The cross-sectional shape of the undulation in a cross section orthogonal to the direction in which the undulation extends has a shape like a kind of sine wave, although the wavelength and the wave height need not be constant. As described above, the cross-sectional shape of both the bottom of the groove and the top of the ridge is curved, so that the surface defect density can be reduced.

  As described above, by providing a plurality of undulations on the substrate surface and the single crystal layer surface, it is possible to obtain the effect of introducing the off-angle shown by K. Shibahara et al. On the slope of each undulation. The distance between the tops of the undulations is preferably 0.01 μm or more from the viewpoint of the limit of the fine processing technology in the preparation of undulations on the substrate and the single crystal layer. If the interval between the tops of the undulations exceeds 1000 μm, the frequency of association between the anti-phase region boundary surfaces is extremely reduced. Therefore, the interval between the tops of the undulations is desirably 1000 μm or less. Further, from the viewpoint that the effect of the present invention is sufficiently exhibited, the interval between the tops of the undulations is preferably 0.1 μm or more and 100 μm or less.

  The undulation height difference and interval influence the undulation inclination, that is, the step density. Although the preferred step density varies depending on the crystal growth conditions, it cannot be said unconditionally. However, the required difference in the height of the undulations is generally the same as the distance between the tops of the undulations, that is, from 0.01 μm to 20 μm. Each undulation is formed so that slopes having a slope of less than 90 ° with respect to the base surface are opposed to each other, and when the inclination angle of the surface with respect to the base surface is integrated over the entire surface, the value is substantially equal. It is preferable that the shape is formed so as to be 0 °.

  In the present invention, the entire substrate and the single crystal layer as described above, or a partial region of the substrate and the single crystal layer (however, this region has the plurality of undulations) is defined as one growth region, Then, a compound single crystal film is continuously formed. By providing undulations of such a shape on the substrate and the single-crystal layer, firstly, as the single-crystal layer is grown on the substrate, the plurality of undulations generated from the steps existing on the slope and growing are formed. Can be associated with each other, and furthermore, by introducing undulations into the single crystal layer, the polar planes appearing on the basal plane are once removed, and the steps formed by the newly formed undulations by the off-slope effect Flow growth results. Therefore, the anti-phase region boundary surface can be effectively eliminated and removed, and a compound single crystal with few defects can be obtained.

  As a method of forming an off-slope on the growth substrate surface (for example, cubic silicon carbide (001) plane), a method of cutting off can be considered. For example, in order to obtain an off-slope of 4 ° at which the off-effect is obtained most. Requires a board thickness of at least 10.5 mm for a 6-inch φ substrate (if a board thickness of 10.5 mm is not obtained, a 6-inch plane area cannot be obtained even when cut at 4 °). In practice, a margin is required when cutting, so it will be 12 to 20 mm thick. However, by performing the undulating process, it is possible to form an off-slope surface facing the 3C-SiC surface having a thickness of several μm, and it is possible to introduce epitaxial growth in a step flow mode.

  In order to form undulations having the above-mentioned shape on the surface of the substrate and the single crystal layer, for example, an optical lithography technique, a press working technique, a laser working, an ultrasonic working technique, a polishing working technique, or the like can be used. Whichever method is used, it is sufficient that the final form of the surface of the substrate to be grown and the single crystal layer have a form sufficient to effectively reduce or eliminate the antiphase region boundary.

  By using an optical lithography technique, an arbitrary undulating shape can be transferred to a substrate to be grown or a single crystal layer by arbitrarily forming a mask pattern to be transferred to a substrate or a single crystal layer. It is possible to control the width of the undulating shape by changing the line width of the pattern, for example, and to control the etching selectivity between the resist and the substrate or the single crystal layer to change the depth of the undulating shape and the angle of the slope. It is possible to control. When forming a substrate in which the shape of a portion where slopes are adjacent to each other is curved in a cross section orthogonal to the direction in which the undulations of the surface of the substrate or the single crystal layer extend, after pattern transfer to the resist, Is softened, it is possible to form an undulating pattern having a cross-sectional curve (wavy shape).

  By using a press working technique, it is possible to form an arbitrary undulation on the substrate to be grown or the single crystal layer by arbitrarily forming a press die. By forming molds of various shapes, various undulating shapes can be formed on the growth target substrate.

When laser processing or ultrasonic processing technology is used, finer processing is possible because the undulating shape is directly formed on the substrate or the single crystal layer.
If the polishing process is used, the width and depth of the undulating shape can be controlled by changing the size of the abrasive grain and the processing pressure of the polishing. When a substrate or a single crystal layer having a one-way undulation is to be manufactured, polishing is performed only in one direction.

  If dry etching is used, the width and depth of the undulating shape can be controlled by changing the etching conditions and the shape of the etching mask. When forming a substrate in which the shape of the portion where the slopes are adjacent to each other is curved in a cross section orthogonal to the direction in which the undulations of the surface of the substrate or the single crystal layer extend, the etching mask is arranged away from the pattern transfer substrate. By doing so, the etching is diffused between the mask and the substrate or the single crystal layer, so that a wavy pattern having a curved cross section can be transferred. Further, the mask may have a trapezoid in which the cross section of the window of the mask is divergent toward the pattern transfer substrate side.

  In the manufacturing method of the present invention, the formation of the undulation on the surface of the single crystal layer and the formation of a new single crystal layer on the single crystal layer having the undulation are performed at least once. The formation of undulations on the surface of the single crystal layer and the formation of a new single crystal layer can be repeated twice or more, for example, in the range of 2 to 10 times. However, if necessary, it can be performed more than 10 times.

In the manufacturing method of the present invention, the directions of the plurality of undulations extending on the surface of the single crystal substrate and the directions of the plurality of undulations provided on the surface of the compound single crystal layer formed on the surface of the substrate are the same. Or they may be orthogonal. Also, even if the directions of the plurality of undulations extending on the surface of a single crystal layer and the directions of the plurality of undulations provided on the surface of the compound single crystal layer formed on the surface of the single crystal layer are the same. , May be orthogonal.
FIG. 1 shows a case where the direction of the plurality of undulations extending on the surface of the Si substrate and the direction of extension of the undulations provided on the surface of the compound single crystal layer formed on the surface of the substrate are the same. In this method, a plurality of undulations extending on the surface of the Si substrate are formed in 1), a compound single crystal layer formed on the surface of the substrate is formed in 2), and a surface of the compound single crystal layer is formed in 3). Are provided (the extending direction of the undulation is the same as the extending direction of the undulation extending on the surface of the Si substrate), and in 4), a compound single crystal layer is further formed.
FIG. 2 shows a case where the directions of the plurality of undulations extending on the surface of the Si substrate and the direction of extension of the plurality of undulations provided on the surface of the compound single crystal layer formed on the surface of the substrate are orthogonal to each other. In this method, a plurality of undulations extending on the surface of the Si substrate are formed in 1), a compound single crystal layer formed on the surface of the substrate is formed in 2), and a surface of the compound single crystal layer is formed in 3). Are provided (the extending direction of the undulations is orthogonal to the extending direction of the undulations extending on the surface of the Si substrate), and in 4), a compound single crystal layer is further formed.

For example, the direction of the undulation formed on the surface of the n-th layer substrate or the single crystal layer matches the direction of the undulation formed on the surface of the (n + 1) th single crystal layer, and the crystal of the n-th layer When the polar plane and the polar plane having the same polarity of the crystal of the (n + 1) th layer are oriented in the same direction, defects propagate from the crystal layer of the (n) th layer to the (n + 1) th layer. There is an effect that it is possible to suppress the generation by actively performing the step flow growth.
Further, the direction of the undulations formed on the surface of the n-th layer substrate or the single crystal layer and the direction of the undulations formed on the surface of the (n + 1) th single crystal layer are the same, and the surface of the (n + 1) th single crystal layer is formed. The direction of the undulations formed on the surface of the n + 2th single crystal layer is orthogonal to the direction of the undulations formed on the surface of the n + 2th single crystal layer. The directions of the undulations formed on the surface of the (n + 1) th single crystal layer are made orthogonal to the undulations formed on the surface of the (n + 1) th single crystal layer and the undulations formed on the surface of the (n + 2) th single crystal layer. May have the same orientation.
In either case, the direction of the formed steps, terraces, and polarity is changed, and the growth direction is forcibly changed, thereby suppressing the propagation of plane defects to the growth layer, and eliminating the plane defects. The effect is increased, and a crystal layer with fewer defects can be obtained.

According to the manufacturing method of the present invention, silicon carbide having a low defect density can be obtained. The elimination of the propagating surface defect from the interface reduces the occurrence of leak current and the like in various electrical characteristics, and makes it possible to use the semiconductor material as a semiconductor material.
Furthermore, according to the production method of the present invention, a compound crystal of gallium nitride on silicon carbide or aluminum nitride on silicon carbide having a low defect density can be obtained.
Furthermore, according to the production method of the present invention, it is possible to obtain hexagonal compound crystals. That is, it is possible to obtain hexagonal silicon carbide, hexagonal gallium nitride, and aluminum nitride with low defect density.
Further, according to the production method of the present invention, it is possible to obtain a high-quality compound crystal having a plane defect density of 1 / cm or less. According to the present invention, a compound crystal which can be sufficiently used as a semiconductor material can be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples.
Example 1
An undulation-formed substrate parallel to the <110> direction was prepared by rubbing an abrasive parallel to the <110> direction on the surface of an Si (001) substrate having a diameter of 6 inches. As the abrasive, a commercially available diamond slurry having a diameter of about 9 μm (High Press manufactured by Engis) and a commercially available polishing cloth (Engis M414) were used. The diamond slurry is uniformly infiltrated into the cloth, the Si (001) substrate is placed on the pad, and a pressure of 0.2 kg / cm ² is applied to the entire Si (001) substrate while the cloth is parallel to the <110> direction. Was reciprocated about 300 times a distance of about 20 cm (unidirectional polishing treatment). Innumerable polishing flaws (undulations) parallel to the <110> direction were formed on the surface of the Si (001) substrate.

  Since the abrasive grains are attached to the surface of the Si (001) substrate which has been subjected to the unidirectional polishing, the substrate is cleaned with an ultrasonic cleaner, and then a mixed solution of hydrogen peroxide and sulfuric acid (1: 1), HF Washed with the solution. After the cleaning, a thermal oxide film of about 1 μm was formed on the undulating substrate under the conditions shown in Table 1 using a heat treatment apparatus. The formed thermal oxide film was removed with diluted hydrofluoric acid. On the substrate surface, many irregularities and defects on fine spikes remained in addition to the undulations to be obtained, and it was difficult to use as a substrate to be grown. However, by forming a thermal oxide film of about 1 μm and removing the oxide film again, the substrate surface was etched by about 2000 °, and fine irregularities were removed, and a very smooth undulation (undulation) could be obtained. . Looking at the wavy cross section, the size of the wavy irregularities is unstable and irregular, but the density is high. It is always in a state of undulation. The groove had a depth of 30 to 50 nm and a width of 1 to 2 μm. The slope was 3-5 °.

  Silicon carbide (3C-SiC) was formed on the substrate obtained by the above method by a vapor deposition method. Tables 2 and 3 show the growth conditions.

3C-SiC was grown while alternately supplying dichlorosilane and acetylene into the reaction tube. Then, 3C-SiC having a thickness of about 200 μm was obtained on the undulated Si substrate. The surface is smooth and mirror-finished, and the undulating shape formed on the underlying substrate does not appear on the surface.
The etch pit density and twin density of the obtained 3C-SiC were determined as follows.
After exposing the 3C-SiC to molten KOH (500 ° C, 5 minutes), the surface was observed with an optical microscope. As a result, there were 1290 etch pits on the entire surface of 6 inches, which seemed to be stacking faults and surface defects (Twin, APB). / cm ² . Further, a pole figure of an X-ray diffraction rocking curve (XRD) for the 3C-SiC (111) plane was prepared, and the signal intensity of the {115} plane orientation corresponding to the twin plane and the normal single crystal plane {111} plane orientation were compared. The twin density was calculated from the signal intensity ratio. As a result, the twin density was found to be 3 × 10 ⁻³ Vol.%.

  Subsequently, undulations similar to those formed on the Si substrate were formed on the 3C-SiC obtained above. The forming method is exactly the same as that described above. The extending direction of the undulation was parallel to the <110> direction. Then, 3C-SiC was homoepitaxially grown to a thickness of 100 μm on the undulated 3C-SiC.

The etch pit density and twin density of the obtained 3C-SiC were determined as follows.
After exposing the 3C-SiC to molten KOH (500 ° C, 5 minutes), the surface was observed with an optical microscope. As a result, there were 420 etch pits that appeared to be stacking faults and surface defects (Twin, APB) on a 6-inch surface, 2.4 / cm ² . Further, a pole figure of an X-ray diffraction rocking curve (XRD) for the 3C-SiC (111) plane was prepared, and the signal intensity of the {115} plane orientation corresponding to the twin plane and the normal single crystal plane {111} plane orientation were compared. The twin density was calculated from the signal intensity ratio. As a result, the twin density was found to be 4 × 10 ⁻⁴ Vol.% Or less, which is the measurement limit.

For comparison, 3C-SiC was continuously formed to a thickness of 300 μm on the undulated Si substrate. After exposing this 3C-SiC to molten KOH (500 ° C, 5 minutes), when observing the surface with an optical microscope, it was found that there were 900 stack pits that appeared to be stacking faults and surface defects (Twin, APB) on the entire surface of 6 inches, It was 5.1 / cm ² . Further, a pole figure of an X-ray diffraction rocking curve (XRD) for the 3C-SiC (111) plane was prepared, and the signal intensity of the {115} plane orientation corresponding to the twin plane and the normal single crystal plane {111} plane orientation were compared. The twin density was calculated from the signal intensity ratio. As a result, the twin density was found to be 2 × 10 ⁻³ Vol.% Or less.
From the above results, it can be understood that the surface defects propagated from the substrate interface to the growth layer surface can be eliminated at an early stage by performing the undulation processing on the growth layer surface and growing 3C-SiC thereon.

Example 2
An attempt was made to produce an undulation-formed substrate parallel to the <110> direction by a method of rubbing an abrasive in parallel with the <110> direction on the surface of a 6-inch-diameter Si (001) substrate. As the abrasive, a commercially available diamond slurry having a diameter of about 9 μm (High Press manufactured by Engis) and a commercially available polishing cloth (Engis M414) were used. The diamond slurry is uniformly infiltrated into the cloth, the Si (001) substrate is placed on the pad, and a pressure of 0.2 kg / cm ² is applied to the entire Si (001) substrate while the cloth is parallel to the <110> direction. Was reciprocated about 300 times a distance of about 20 cm (unidirectional polishing treatment). Innumerable polishing flaws (undulations) parallel to the <110> direction were formed on the surface of the Si (001) substrate.

  Since polishing abrasive grains and the like are attached to the surface of the Si (001) substrate that has been subjected to the one-way polishing, cleaning is performed using an ultrasonic cleaner, and then, a mixed solution of hydrogen peroxide and sulfuric acid (1: 1) is used. Washed with HF solution. After cleaning, a thermal oxide film was formed to a thickness of about 1 μm on the undulating substrate under the conditions shown in the table using a heat treatment apparatus. The formed thermal oxide film was removed with diluted hydrofluoric acid. In addition to the undulations to be obtained, many irregularities and defects on fine spikes remain on the substrate surface, making it difficult to use as a substrate to be grown. However, by forming a thermal oxide film of about 1 μm and removing the oxide film again, the substrate surface was etched by about 2000 °, and fine irregularities were removed, and a very smooth undulation (undulation) could be obtained. . Looking at the wavy cross section, the size of the wavy irregularities is unstable and irregular, but the density is high. It is always in a state of undulation. The groove had a depth of 30 to 50 nm and a width of 1 to 2 μm. The inclination was generally in the range of 3 to 5 °, although there was variation in each inclination.

A 200 μm thick 3C-SiC was grown on the undulated Si (001) substrate thus fabricated. The forming conditions are as shown in Tables 2 and 3.
The obtained 3C-SiC surface was subjected to undulation processing. The undulating extension direction was parallel to the <1-10> direction. That is, the extending direction of the undulations formed on the base substrate is a direction orthogonal to the case where the sample is viewed in the <001> direction.

3C-SiC was homoepitaxially grown to a thickness of 100 μm on the 3C-SiC obtained above. The growth method is the same as the method described above.
The etch pit density and twin density of the obtained 3C-SiC were determined as follows.
After exposing the 3C-SiC to molten KOH (500 ° C, 5 minutes), the surface was observed with an optical microscope. As a result, stacking defects and surface defects (Twin, APB) were found to have 380 etch pits on a 6-inch surface, 2.2 / cm ² . Further, a pole figure of an X-ray diffraction rocking curve (XRD) for the 3C-SiC (111) plane was prepared, and the signal intensity of the {115} plane orientation corresponding to the twin plane and the normal single crystal plane {111} plane orientation were compared. The twin density was calculated from the signal intensity ratio. As a result, the twin density was found to be 4 × 10 ⁻⁴ Vol.% Or less, which is the measurement limit.

Example 3
In this embodiment, undulation processing was performed on the 3C-SiC obtained in Embodiment 2. The processing method is the same as the method of the second embodiment. Then, 100 μm thick 3C-SiC was epitaxially grown on the undulating 3C-SiC surface. The growth method is the same as that of the second embodiment.

The etch pit density and twin density of the obtained 3C-SiC were determined as follows.
After exposing 3C-SiC to molten KOH (500 ° C, 5 minutes), the surface was observed with an optical microscope. As a result, the number of stack pits and surface defects (Twin, APB) was 240 in 6 inches and 1.36 in total. / cm ² . Furthermore, X-ray diffraction rocking curve (XRD) for 3C-SiC <111> orientation was observed at the extreme points, and signal intensity of {115} plane orientation corresponding to twin plane and signal of normal single crystal plane {111} plane orientation were observed. The twin density was calculated from the intensity ratio. As a result, the twin density was found to be 4 × 10 ⁻⁴ Vol.% Or less, which is the measurement limit.

Example 4
An attempt was made to produce an undulation-formed substrate parallel to the <110> direction by a method of rubbing an abrasive in parallel with the <110> direction on the surface of a 6-inch-diameter Si (001) substrate. As the abrasive, a commercially available diamond slurry having a diameter of about 9 μm (High Press manufactured by Engis) and a commercially available polishing cloth (Engis M414) were used. The diamond slurry is uniformly infiltrated into the cloth, the Si (001) substrate is placed on the pad, and a pressure of 0.2 kg / cm ² is applied to the entire Si (001) substrate while the cloth is parallel to the <110> direction. Was reciprocated about 300 times a distance of about 20 cm (unidirectional polishing treatment). Innumerable polishing flaws (undulations) parallel to the <110> direction were formed on the surface of the Si (001) substrate.

  Since polishing abrasive grains and the like are attached to the surface of the Si (001) substrate that has been subjected to the one-way polishing, cleaning is performed using an ultrasonic cleaner, and then, a mixed solution of hydrogen peroxide and sulfuric acid (1: 1) is used. Washed with HF solution. After cleaning, a thermal oxide film was formed to a thickness of about 1 μm on the undulating substrate under the conditions shown in the table using a heat treatment apparatus. The formed thermal oxide film was removed with diluted hydrofluoric acid. In addition to the undulations to be obtained, many irregularities and defects on fine spikes remain on the substrate surface, making it difficult to use as a substrate to be grown. However, by forming a thermal oxide film of about 1 μm and removing the oxide film again, the substrate surface was etched by about 2000 °, and fine irregularities were removed, and a very smooth undulation (undulation) could be obtained. . Looking at the wavy cross section, the size of the wavy irregularities is unstable and irregular, but the density is high. It is always in a state of undulation. The groove had a depth of 30 to 50 nm and a width of 1 to 2 μm. The slope was 3-5 °.

Silicon carbide (3C-SiC) was formed on the substrate obtained above by a vapor deposition method. Tables 2 and 3 show the growth conditions.
3C-SiC was grown while alternately supplying dichlorosilane and acetylene into the reaction tube. Then, 3C-SiC having a thickness of about 200 μm was obtained on the undulated Si substrate. The surface is smooth and mirror-finished, and the undulating shape formed on the underlying substrate does not appear on the surface.

The etch pit density and twin density of the obtained 3C-SiC were determined as follows.
After exposing the 3C-SiC to molten KOH (500 ° C, 5 minutes), the surface was observed with an optical microscope. As a result, there were 1290 etch pits on the entire surface of 6 inches, which seemed to be stacking faults and surface defects (Twin, APB). / cm ² . Furthermore, X-ray diffraction rocking curve (XRD) for 3C-SiC <111> orientation was observed at the extreme points, and signal intensity of {115} plane orientation corresponding to twin plane and signal of normal single crystal plane {111} plane orientation were observed. The twin density was calculated from the intensity ratio. As a result, the twin density was found to be 3 × 10 ⁻³ Vol.%.

An attempt was made to form gallium nitride (GaN) by performing relief processing on the 3C-SiC obtained above. Trimethylgallium and ammonia were supplied by a metal organic chemical vapor deposition (MOCVD) apparatus to form GaN. The growth temperature was 1100 ° C., 20 slm of nitrogen, 10 slm of ammonia (NH ₃ ) and 1 × 10 ⁻⁴ mol / min of trimethylgallium were supplied as carrier gases. The thickness is about 10 μm.

The twin density of the obtained GaN was determined as follows.
Create a pole figure of the X-ray diffraction rocking curve (XRD) for the GaN (111) plane, and compare the signal intensity of the {115} plane orientation corresponding to the twin plane to the signal intensity of the normal single crystal plane {111} plane The twin density was calculated from. As a result, the twin density was found to be 4 × 10 ⁻⁴ Vol.% Or less, which is the measurement limit.

As a comparative example, GaN was formed on 3C-SiC that was not subjected to undulation processing. The formation was performed in the same manner as described above. The defect density of the obtained GaN was determined as follows. Create a pole figure of the X-ray diffraction rocking curve (XRD) for the GaN (111) plane, and compare the signal intensity of the {115} plane orientation corresponding to the twin plane to the signal intensity of the normal single crystal plane {111} plane The twin density was calculated from. As a result, it was found that the twin density was 5 × 10 ⁻³ Vol.%.

Scheme of the manufacturing method of the present invention in the case where the directions of the plurality of undulations extending on the surface of the Si substrate and the direction of extension of the undulations provided on the surface of the compound single crystal layer formed on the surface of the substrate are the same. Is shown. The scheme of the manufacturing method of the present invention in the case where the direction of the plurality of undulations extending on the surface of the Si substrate and the direction of extension of the plurality of undulations provided on the surface of the compound single crystal layer formed on the surface of the substrate are orthogonal. Show. Schematic view of a tilted (off-angle introduced) silicon (001) surface substrate. FIG. 4 is an explanatory view of a conventional method for making a substrate slightly inclined. FIG. 4 is an explanatory view showing a state in which a surface defect propagating in silicon carbide is eliminated in a method in which silicon carbide is epitaxially grown on a substrate which has been subjected to undulating processing and whose off-slopes are opposed to each other. In a method in which silicon carbide is epitaxially grown on a substrate which has been subjected to undulation and whose off-slopes are opposed to each other, a state in which surface defects propagating into silicon carbide are eliminated (facing surface defects are associated with each other and disappear). FIG. FIG. 4 is an explanatory diagram of an angle formed between a {111} plane, which is a plane of a defect to be eliminated in a cubic crystal layer, and a (001) plane, which is a growth plane (horizontal plane).

Claims (7)

A method for producing a compound single crystal, wherein two or more layers of the same or different compound single crystal layers are sequentially epitaxially grown on the surface of a single crystal substrate,
At least a portion of the substrate surface has a plurality of undulations extending in one direction, and the second and subsequent epitaxial growths extend in one direction on at least a portion of the surface of the compound single crystal layer formed immediately before. Performing the method after forming a plurality of undulations. 2. The compound single crystal layer according to claim 1, wherein the compound single crystal layer is a compound single crystal different from the single crystal substrate, and the compound single crystal forming the compound single crystal layer and the single crystal forming the single crystal substrate have a similar spatial lattice. Manufacturing method. The direction of the plurality of undulations extending on the surface of the single crystal substrate and the direction of extension of the undulations provided on the surface of the compound single crystal layer formed on the surface of the substrate are the same or orthogonal. Manufacturing method. The manufacturing method according to any one of claims 1 to 3, wherein the extending directions of the plurality of undulations provided on the surface of the compound single crystal layer provided adjacent to the growth direction are the same or orthogonal. The method according to claim 1, wherein the single-crystal substrate is single-crystal SiC. The method according to any one of claims 1 to 5, wherein the compound single crystal layer is single crystal SiC, or gallium nitride, aluminum nitride, or aluminum gallium nitride. The single-crystal SiC substrate is cubic SiC whose basal plane is a (001) plane, or hexagonal SiC whose basal plane is a (11-20) plane or a (1-100) plane. 7. The production method according to any one of 6.

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